New full paper in Small

posted Nov 12, 2013, 9:45 PM by Shin-Hyun Kim
Shin-Hyun Kim, Tae Yong Lee and Sang Seok Lee, "Osmocapsules for Direct Measurement of Osmotic Strength," Small, accepted for publication (2013). (Corresponding author)

Monodisperse microcapsules with ultra-thin membrane are microfluidically-designed to be highly sensitive to osmotic pressure, thereby providing a tool for direct measurement of osmotic strength. To make such osmocapsules, water-in-oil-in-water double-emulsion drops with ultra-thin shell are prepared as templates through emulsification of core-sheath biphasic flow in a capillary microfluidic device. When photocurable monomers are used as oil phase, the osmocapsules are prepared by in-situ photopolymerization of the monomers, resulting in semipermeable membranes with relatively large ratio of membrane thickness to capsule radius, approximately 0.02. These osmocapsules are buckled by outward flux of water when they are subjected to positive osmotic pressure difference above 125 kPa. By contrast, evaporation-induced consolidation of middle phase containing polymers enables the production of osmocapsules with small ratio of membrane thickness to capsule radius as approximately 0.002. Such ultra-thin membrane with semi-permeability makes the osmocapsules highly sensitive to osmotic pressure; positive pressure as small as 12.5 kPa induces buckling of the capsules. By employing a set of distinct osmocapsules confining aqueous solutions with different osmotic strengths, the osmotic strength of unknown solutions can be estimated through observation of the capsules which are selectively buckled. This approach provides the efficient measurement of osmotic strength with very small volume of liquid, thereby providing a useful alternative to other measurement methods which use complex setups. In addition, in-vivo measurement of the osmotic strength can be potentially accomplished by implanting these biocompatible osmocapsules into tissue, which is difficult to achieve in conventional methods.